Pitot tube



A ril 9, 1963 c. w. FINKL ETA]. 3,084,543

PITOT TUBE Filed June 1, 1959 IN V EN TORS Uni atent 3,084,543 PITOTTUBE Charles W. Finkl and Arthur Carlson, Chicago, lib, as-

signors, by mesne assignments, to Attwood Corporation, a corporation ofMichigan Filed June 1, 1959, Ser. No. 817,342 11 Claims. (Cl. 73-182)Our invention relates generally to water speed measuring devices andparticularly to a new and improved Pitot tube for water speedindicators.

Pitot tubes for pleasure boat Water speed indicators are generallymounted on the boat near the bottom of the transom. A water passageextends through the tube and has an admission port opening in thedirection of boat travel at the lower end. The upper end opens into aconduit leading to a pressure gauge. As the boat moves forward, waterflows up the passage and through the conduit to the pressure gauge whichis calibrated in water speed units.

Pitot tubes are generally one of the lowest hanging projections from theboat. They should be able to kick upwardly upon contact with floatingdriftwood, dead heads or other underwater objects and then swing backdown into a centered or equilibrium condition to provide a continuouslyaccurate reading. In efiect, the tube must automatically reset itselfafter the disrupting object has passed. The tube must also be capable ofbeing mounted on transoms of varying angles, must maintain perfectlyhorizontal alignment even when the boat porpoises or changes its planingangle, and must be ble to shed weeds easily.

Most present Pitot tubes generally utilize a spring arrangement forresetting the tube after a foreign object passes. These tubes aresubject to failure due to repeated flexure from impact with underwaterobjects and the action of the water on the tube. After a time the springconstant decreases to a point where it may not be able to hold the tubeperfectly horizontal and false readings result.

Accordingly, a primary object of this invention is to provide a Pitottube which utilizes water forces acting on the tube to maintain itproperly positioned at all speeds.

Another object is to provide a light, compact Pitot tube which swings upon impact with a foreign object in the water and automatically resetsitself as the object passes by without the use of springs.

Another object is to provide a Pitot tube which may be mounted on atransom of any angle.

Yet another object is to provide a Pitot tube which stays in perfectalignment even though the boat porpoises or changes its planing angle.

Yet a further object is to provide a Pitot tube which may be fabricatedfrom inexpensive plastic material.

Another object is to provide a combination hydraulicpneumatic Pitot tubeassembly having a pressure stabilizer which instantly and accuratelyreflects changes in speed.

Other objects and advantages of our invention will become apparent fromthe following description taken in connection with the accompanyingdrawings wherein by way of illustration and example certain embodimentsof the invention are set forth.

Our invention is illustrated more or less diagrammatically in theaccompanying drawings wherein:

FIGURE 1 is a side view of our Pitot tube mounted on the lower portionof a transom;

FIGURE 2 is a rear view of the Pitot tube of FIG- URE 1;

FIGURE 3 is a bottom view of the Pitot tube of FIG- URE 1;

' the bottom as illustrated in FIGURE 1.

FIGURE 4 is a side view of another embodiment of our Pitot tubeillustrating a pressure stabilizing tank; and

FIGURE 5 is a bottom view of the Pitot tube of FIG- URE 4.

Like reference numerals will be used to indicate like parts throughoutthe specification and drawings.

In FIGURE 1, our Pitot tube is indicated generally at 10. It includes abody or shank portion :11, a mounting ear 12 at the upper inner edge ofthe shank portion, and a foot or paravane 13 at the bottom. The shankportion 11 has knife edges 14 and 15 on the leading and trailing edgesrespectively to present minimum water resistance. Trailing edge 15 iscontoured into the paravane to provide non-turbulent water flow. Asplash plate 16 deflects the water downwardly as the tube moves throughthe water.

Paravane 13 in this instance is roughly in the form of an isoscelestriangle with the apex of the equal sides terminating near the bottom ofleading edge 14. Top surface 17 is slightly inclined from the horizontalto form a sharp edge with bottom surface 18 as at 19.

Water passage or aperture 29 extends through the body. Admission port 21opens into the blunt end of thickened portion 22 of the vane. Outlet 23at the top of the body is adapted for connection to a water speedindicator. The sharp edge 19 extends horizontally outwardly on each sideof the blunt end of thickened portion 22 so the paravane will morereadily dig into the water after having been kicked upwardly.

The Pitot tube is secured to transom 24 by an automatic reset clipindicated generally at .25. The clip includes a roughly oval shaped backplate 26 and a pair of parallel ears 27 and 28. The ears form a slot 29slightly larger than the width of mounting ear 12. Each clip ear has aninwardly and downwardly tapered recess 30, 31 opening into circularrecesses 32, 33. The bottom width of the tapered recesses may beslightly smaller than the diameter of the circular recess. Pivot pin 34which may be fixed or rotatable in mounting ear 12 slips into thecircular recesses 32, 33 to permit swinging movement of the tube. Screws37 fasten the bracket to the transom.

A variation of our invention is illustrated in FIGURES 4 and 5. Circularplatform 40 rests on splash plate 16 and a fluid tight pressurestabilizing or static tank 41 is secured thereto. Hose 42 connects thetank to any suitable water speed indicator 43-.

The water aperture 44 in this instance slants upwardly from the inletport '45 through the circular platform 40 and opens into the tank. Thiseliminates the elbow at The leading edge of paravane 50, which isconsiderably larger than paravane 13, is streamlined as at 51 to reducewater resistance. The trailing edge is extended as at 52 for a purposewhich will appear hereafter.

The use and operation of the invention is as follows:

Pitot tubes determine the speed of a boat relative to the water bymeasuring the impact or force of the water on the tube. The magnitude ofthe force varies roughly proportionally to the square of the relativeboat-water speed as expressed by the formula V= /2-gh where V is feet/second, g is gravity, and h is head of water in feet. The force is thentransmitted to a pressure gauge calibrated to read directly in waterspeed units.

In FIGURE 1, water enters the tube through inlet port 21, passesupwardly through passage 20 and enters a hose connected to outlet port23 leading to a pressure gauge (not shown). No matter what speed theboat is moving through the water, the tube will maintain the position ofFIGURE 1 and 2 for the following reason.

Force vector R represents the reaction of the center of pressure of thewater on the vane 13. This value be mathematically determined from thedimensions and angle of incidence of the vane. X represents the distancefrom the pivot point P to the point at which R acts on vane 13. Forcevector Cl? represents the force acting against that portion of the Pitottube against whicl the water impinges. For convenience of illustration,all the force is illustrated as acting through the center of pressurewhich can be mathematically determined once the dimensions of the Pitottube are known. Y repre sents the perpendicular distance between thepivot point P and the center of pressure.

counterclockwise moment RX must equal clockwise moment (CP) Y for thePitot tube to remain in the position of FIGURE 1. This condition ofequilibrium will always be attained because as the tube swings eitherrearwardly or forwardly, the moments become unbalanced with the largermoment always acting in an equilibrium restoring direction.

If an unbalanced condition occurs whereby the Pitot tube movesrearwardly, the tube swings clockwise about pin 34. Force R willincrease since the angle of incidence of vane 13 increases. Distance Xalso increases. At the same time force (CP) decreases since theeffective area of the body portion decreases as it swings upwardly fromits FIGURE 2 position. Distance Y also decreases. The largercounterclockwise moment XR then swings the tube back to the FIGURE 1position.

Similarly, should the tube swing forward for any reason as for examplewhen the mounting bracket is secured to an upwardly and rearwardlyinclined transom, X decreases, force R acts in a reverse direction andboth Y and (CP) increase, thus setting up unbalanced clockwise moments.These unbalanced moments quickly reposition the tube.

A pneumatic-hydraulic pressure stabilized tube assembly is illustratedin the embodiment of FIGURES 4 and 5. When water alone is utilized thewater speed indicator tends to read slow because the pressure gauge 43is not instantly responsive to changes in water pressure resulting fromchanges in boat speed. This is because the static head of water mustrise from the level of the tube to the pressure gauge before the needleis actuated. Static tank 41 converts the static head to a more sensitivecombined hydraulic-pneumatic head. As the water level in tank 41 rises,which will occur substantially instantaneously with changes in boatspeed because of the relatively short passage 44, the air in the spaceabove water W will be simultaneously compressed. The change in airpressure is then instantly read on air pressure responsive gauge 43.

Extended portion 52 of paravane 50 increases the downwardly acting forceR to more quickly reposition the tube. Additional vanes may be added ifneeded.

Since the Pitot tube assembly automatically resets itself solely inresponse to water forces acting on it, no springs are needed to returnit to normal operating position. Consequently mounting bracket 25 may bemade of inexpensive plastic materials which do not induce electrolyticdeterioration of the hull. The tube itself may be molded from plasticsince no inherent spring action is required.

The downwardly and rearwardly tapered leading edge sheds weeds andpresents a sliding edge to driftwood, dead heads and other underwaterobjects whereby the tube may be kicked up without any possibility ofbinding or catching upon the object.

As will be readily apparent to one skilled in the art, the Pitot tubeshould be located in a position in which it is exposed only toundisturbed water flow. It is well known, for example, that the area ofturbulence formed behind a propeller is cone shaped, and hence it isdesirable to position the Pitot tube out of this turbulent cone shapedarea for most accurate readings. Similarly, the tube should not bepositioned in the turbulent area directly behind any downwardly hangingobstruction.

can

Other variations will be apparent to those slc lled in the art. Forexample, any suitable structure may be utilized to permit free swingingmovement of the assembly about the pivot point P. We have formedspherical segments I on either side of the mounting ear 1?. in place ofPivot pin 34 for example.

The foregoing description is illustrative only and not definitive.Accordingly, our invention should not be limited except by the scope ofthe following appended claims.

We claim:

1. An automatically self stabilizing Pitot tube which utilizes waterforces to maintain it properly positioned at *all speeds and planingangles of the boat to which it is attached, said Pitot tube including abody member adapted to be pivotally mounted to a boat whereby a portionof the member is submerged, said member having a passage extendingtherethrough, said passage having a water admission port in thesubmerged portion opening substantially in the direction of travel ofthe boat and an outlet adapted to be connected to a suitable gauge, anda generally horizontally oriented paravane on the submerged portion ofthe body, said paravane being so positioned that the moment tending toswing the tube about the pivot in one direction due to the downwardlyacting force on the paravane balances the moment tending to swing thetube about the pivot in the opposite direction due to the rearwardlyacting force of the water when the boat moves relative to the water.

2. The Pitot tube of claim 1 further including a mounting member adaptedto be secured to a boat, the Pitot tube being pivotally mounted in themounting member.

3. The Pitot tube of claim 1 in which the water admission port is in theleading edge of the paravane.

4. The Pitot tube of claim 3 in which the paravane diverges outwardlyrearwardly, the leading edge having a thickened center portion in whichthe water admission port is formed flanked by knife edges to facilitatereentry of the paravane into the water after being kicked upwardly.

5. The automatically self-stabilizing Pitot tube of claim 1 furthercharacterized in that the paravane is formed with a rearwardly, upwardlyinclined top surface.

6. The Pitot tube assembly of claim 1 further characterized in that thepassage has a substantially straight run from the water admission portto the outlet.

7. A Pitot tube assembly for use with a water speed indicator, saidassembly including, in combination, a body member adapted to bepivotally mounted on a boat whereby a portion of the body member issubmerged, said member having a passage extending therethrough, saidpassage having its inlet in the submerged portion opening substantiallyin the direction of travel of the boat and its outlet opening into apressure stabilizing tank communicating with the outlet, said tankhaving an air outlet adapted for connection to an air pressureresponsive water speed indicator, and a vane on the submerged portion ofthe body member, said vane being so positioned that the moment tendingto swing the assembly about the pivot in one direction due to thedownwardly acting force on the vane balances the moment tending to swingthe assembly about the pivot in the opposite direction due to therearwardly acting force of the water when the boat moves relative to theWater.

8. The Pitot tube assembly of claim 7 further characterized in that thepassage has a substantially straight run from its inlet to the outletcommunicating with the tank.

9. The Pitot tube assembly of claim 7 further characterized in that theinlet is in the leading edge of the vane, and further including a splashplate near the upper edge of the submerged portion of the body member.

10. An automatically self stabilizing Pitot tube which utilizes watercreated pressure forces to maintain it properly positioned at all speedsand planing angles of a boat to which it is attached and whichautomatically re- 5 r sets itself after encountering an obstruction,said Pito tube including, in combination,

a body member having a passage therein, said passage having a wateradmission port opening in the direction of boat travel and an outletadapted for connection to a pressure responsive speed indicating device,

pivot means for mounting the body member to the boat, said pivot meansbeing arranged to enable the body member to swing freely in response toimpact with objects in its path of movement and to changes in positionand planing angle of the boat, at least that portion of the body memberhaving the water admission port therein being constructed and arrangedto be submerged at all times during normal, unimpeded operation,

a generally horizontally oriented paravane near the bottom of thesubmerged portion,

said paravane being effective, due to water forces acting thereagainst,to induce a moment tending to swing the Pitot tube about the pivot meansin opposition to a moment tending to swing the Pitot tube in theopposite direction due to water forces acting against the submergedportion of the Pitot tube.

11. The automatically self stabilizing Pitot tube of claim 10 furthercharacterized in that the water admission port opens into the leadingedge of the paravane, said leading edge having a thickened centerportion in which the water admission port is formed flanked by sharpedges which facilitate re-entry of the paravane into the water afterhaving been kicked upwardly.

References Cited in the file of this patent UNITED STATES PATENTS382,362 Hogg May S, 1888 672,123 Delanoy Apr. 16, 1901 1,099,206 SanbornJune 9, 1914 1,955,502 Kenyon Apr. 17, 1934 2,617,297 Moore Nov. 11,1952

10. AN AUTOMATICALLY SELF STABILIZING PITOT TUBE WHICH UTILIZES WATERCREATED PRESSURE FORCES TO MAINTAIN IT PROPERLY POSITIONED AT ALL SPEEDSAND PLANING ANGLES OF A BOAT TO WHICH IT IS ATTACHED AND WHICHAUTOMATICALLY RESETS ITSELF AFTER ENCOUNTERING AN OBSTRUCTION, SAIDPITOT TUBE INCLUDING, IN COMBINATION, A BODY MEMBER HAVING A PASSAGETHEREIN, SAID PASSAGE HAVING A WATER ADMISSION PORT OPENING IN THEDIRECTION OF BOAT TRAVEL AND AN OUTLET ADAPTED FOR CONNECTION TO APRESSURE RESPONSIVE SPEED INDICATING DEVICE, PIVOT MEANS FOR MOUNTINGTHE BODY MEMBER TO THE BOAT, SAID PIVOT MEANS BEING ARRANGED TO ENABLETHE BODY MEMBER TO SWING FREELY IN RESPONSE TO IMPACT WITH OBJECTS INITS PATH OF MOVEMENT AND TO CHANGES IN POSITION AND PLANING ANGLE OF THEBOAT, AT LEAST THAT PORTION OF THE BODY MEMBER HAVING THE WATERADMISSION PORT THEREIN BEING CONSTRUCTED AND ARRANGED TO BE SUBMERGED ATALL TIMES DURING NORMAL, UNIMPEDED OPERATION, A GENERALLY HORIZONTALLYORIENTED PARAVANE NEAR THE BOTTOM OF THE SUBMERGED PORTION, SAIDPARAVANE BEING EFFECTIVE, DUE TO WATER FORCES ACTING THEREAGAINST, TOINDUCE A MOMENT TENDING TO SWING THE PITOT TUBE ABOUT THE PIVOT MEANS INOPPOSITION TO A MOMENT TENDING TO SWING THE PITOT TUBE IN THE OPPOSITEDIRECTION DUE TO WATER FORCES ACTING AGAINST THE SUBMERGED PORTION OFTHE PITOT TUBE.